Method of heat treating cerium-iron alloys



United States Patent METHOD OF HEAT TREATING CERlUM-IRON ALLOYS WalterBungardt, Essen-Bredeney, Germany, assignor to Th. Goldschmidt A.-G.Chemische Fabriken, Essen, Germany No Drawing. Application March 31,1954, Serial No. 420,191

3 Claims. (Cl. 148-13 This invention relates to a method of heattreating cerium iron alloys.

Pyrophoric metals of the cerium-iron alloy type which are used, forexample, for the production of flints for lighters or similar purposeshave been known for a long time. Mischmetal may be employed in place ofcerium in producing the flint compositions and comprises a mixture of apredominant part of cerium with other rare earth elements such aslanthanum. It is also known to improve the useful properties of suchalloys, for example, their resistance to decomposition when stored atroom temperature or moderately elevated temperatures or else the formand nature of sparkingetfect and like properties, by further alloyingadditions or ingredients in relatively small amounts. Copper, magnesium,zinc, silicon, tin and many other elements have previously been proposedfor this and similar purposes.

It is also known that the mode and quantity of further additions to thealloy, such as those hereinabove mentioned, depend upon the process formanufacturing these flint metal alloys. The extrusion process generallynecessitates a diiferent flint composition from that employed incasting. Copper and/or zinc should be excluded from compositionsintended for extrusion as they form a molten alloy at the optimumtemperature required for extrusion of the basic components constitutingthe flint alloy.

Flints can be produced by casting or extrusion. In the former case theyare shaped by a special casting process using special moulds. In thecase of extrusion the starting material is a suitably composed ingot, asdisclosed in U. S. Patent No. 2,660,301, which is converted into thedesired final dimensions of the flint in an extrusion press atrelatively high and predetermined temperatures and pressures.

Hitherto it has been customary to use flints, produced from mischmetalor cerium-iron alloys by known methods of manufacture, directly asobtained after shaping and cooling to room temperature. The flints aregenerally also given special surface treatment, for example, "throughapplication of a protective coating or covering in order to reducecorrosion; for example, fine aluminum tinsel is applied to the surfaceof the flint and secured thereto by using a lacquer.

These methods, which are carried out at room temperature or moderatelyelevated temperatures, are however without influence on the propertiesof the pyrophoric metal alloy.

It is therefore one of the objects of the present invention to providemeans conducive to considerable improvements in highly desirablestructural, physical and sparking properties of such pyrophoricmaterial.

It is another object of the present invention to provide meansfacilitating the preparation of an alloy of the aforesaid type which ishomogeneous and of substantially reduced hardness and has increasedsparking capa-' bilities.

Still another object of the present invention is to provide meansaffording a relatively inexpensive treatment step for imparting to thealloy enhanced and desirable qualities whereby the excitability andsparking stimulation of the alloy is markedly improved.

These and other objects of the invention will ensue from the furtherdescription thereof and the attached claim or claims.

Referring now more particularly to the present invention in greaterdetail, it is to be noted that surprising results have been observedwhen flints produced by either extrusion or casting are subjected infinished form to thermal after-treatment at elevated temperatures up tothe temperature at which the respective alloy commences to melt.

The novel after-treatment efiects a decrease in the hardness of thealloys utilized along with a simultaneous improvement in theexcitability (pyrophoric sparking) of these alloys.

If, for example, a mischmetalor cerium-iron alloy containing about 10%to 30%.by weight of iron, with or without the customary alloyingadditions of materials such as copper, zinc, silicon, magnesium, tin,and the like, is subjected to an after-treatment at temperaturesranging'between C. and the melting point of the alloy, the pyrophoricproperties are considerably improved while the hardness is somewhatreduced. The preferred temperature range for the after-treatment liesbetween 300 C. and 450 C. which approaches the softening range of thealloy.

The following example is illustrative of the practice of the presentinvention:

EXAMPLE I An alloy containing by weight 18.6% Fe, 1.9% Mg, and 0.8% Sn,the remainder being mischmetal, was subjected to after-treatment at 400C. As a result of this after-treatment, the hardness was decreased fromkg./mm. to 120 kg./mm. As determined at low contact pressures, theexcitability of the alloy was increased from 40% to 90%. At high contactpressures, the excitability of the alloy was increased from 84% to 100%.Insofar as could be observed under the microscope, there were no visiblechanges in the internal structure of the alloy.

While a decrease in hardness will produce an increase in excitability asa purely mechanical effect, the increased excitability achieved by thethermal after-treatment herein described is not due solely to thedecrease in hardness. Rather, it appears that there may be solubilitychanges within the mixed crystal components of the alloy which are notdetectable by a microscope, but which nonetheless cause enhancedexcitability of the alloys.

The following example is a further illustration of. the advantagesderived from thermal after-treatment according to the present invention:

EXAMPLE II An alloy containing by weight 20.2% Fe, 1.8% Mg, and 0.9% Sn,the remainder comprising mischmetal, exhibited, at room temperature, ahardness of kg./mm. the test being carried out with a 0.625 mm. ball,and 11.7 kg. load at 30 sec. load duration. For comparative purposes,after formation the alloy was brought to different temperature levelsand the hardness was determined. In addition, the excitability at bothlow and high contact pressure was determined. The results are tabulatedin the following table:

As carrbe seen from this" table, the hardnessd'ecreases continuously asthe temperature of after-treatment increases to 400 C. In: contrasttherewith, the excitability at both high and low contact pressures(against the flint) decreases with increased temperature ofafter-treatment until a minimum value is attained at' about 300 C.Further increase in the aftentreatment temperature produces a rise inthe excitability to a maximum value at about 400 C. after which theexcitability levels off; This-table indicates thecomplex nature of theimprovement achieved bythe thermal treatments herein de scribed.

It can thus be seen. that there has been-provided according to thisinvention animproved flint alloy and a. novel method of producing sameby subjecting: said alloy (cerium-iron or mischmetal-ironalloy); in itsfin ished form to athermal after-treatment at an= approximatetemperature ranging between 300 CL and 450 C.

before said alloy is allowed to cool down to room temperature.

While preferred forms of? the invention have been described above, itwill be apparent that numerous changes and modifications may be made inthe manner of producing .flint and like alloys in accordance with myinvention without. departing. fromthespirit and scope thereofl Havingthus described the invention, what is claimed as new and desired tobesecured by'Letters Patent; is:

1. The method of improving'properties' offii'nts made from cerium-ironalloy, which comprises subjecting said alloy subsequent to=final rodformation to a.heat'.aftertreatment at a temperature within :the rangebetween C. and approximately the temperature at which melting of saidalloy starts.

2. The method of improving useful properties of flints made frommisehmetal (ceriumQ-iron alloys, which comprises subjecting said alloy,after final formationthcreof into fiint rods, to a. subsequent heattreatment. at a. temperature range between 100 C. and about 400 C.

3. The method of imparting increased. sparking properties to flintalloys, which comprises. exposing. said fiint' alloy after final rod.formation thereof, to a thermal aftertreatment at a. temperature.ranging between 100 C. and about. 450 C. at which latter temperature.melting. of said alloy is initiated.

Hirsch Dec. 31, 19.18

1. THE METHOD OF IMPROVING PROPERTIES OF FLINTS MADE FROM CERIUM-IRONALLOY, WHICH COMPRISES SUBJECTING SAID ALLOY SUBSEQUENT TO FINAL RODFORMATION TO A HEAT AFTERTREATMENT AT A TEMPERATURE WITHIN THE RANGEBETWEEN 100* C. AND APPROXIMATELY THE TEMPERATURE AT WHICH MELTING OFSAID ALLOY STARTS.